注：此功能依赖GD2图形库
最近要用php生成缩略图，在网上找了一下，发现了这篇文章：PHP生成图片缩略图
试用了一下后，发现有这样几个问题：
1、png图片生成的缩略图是jpg格式的
2、png图片生成的缩略图没有了透明（半透明）效果（填充了黑色背景）
3、代码语法比较老
因此，在这个版本的基础上简单修改优化了一下。
PHP生成缩略图类
<?php /* * desc: Resize Image(png, jpg, gif) * author: 十年后的卢哥哥 * date: 2014.11.13 */ class ResizeImage { //图片类型 private $type; //实际宽度 private $width; //实际高度 private $height; //改变后的宽度 private $resize_width; //改变后的高度 private $resize_height; //是否裁图 private $cut; //源图象 private $srcimg; //目标图象地址 private $dstimg; //临时创建的图象 private $im; function __construct($imgPath, $width, $height, $isCut, $savePath) { $this->srcimg = $imgPath; $this->resize_width = $width; $this->resize_height = $height; $this->cut = $isCut; //图片的类型 $this->type = strtolower(substr(strrchr($this->srcimg,"."),1)); //初始化图象 $this->initi_img(); //目标图象地址 $this -> dst_img($savePath); //-- $this->width = imagesx($this->im); $this->height = imagesy($this->im); //生成图象 $this->newimg(); ImageDestroy ($this->im); } private function newimg() { //改变后的图象的比例 $resize_ratio = ($this->resize_width)/($this->resize_height); //实际图象的比例 $ratio = ($this->width)/($this->height); if($this->cut) { //裁图 $newimg = imagecreatetruecolor($this->resize_width,$this->resize_height); if($this->type=="png") { imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127)); } if($ratio>=$resize_ratio) { //高度优先 imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width,$this->resize_height, (($this->height)*$resize_ratio), $this->height); } else { //宽度优先 imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, $this->resize_height, $this->width, (($this->width)/$resize_ratio)); } } else { //不裁图 if($ratio>=$resize_ratio) { $newimg = imagecreatetruecolor($this->resize_width,($this->resize_width)/$ratio); if($this->type=="png") { imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127)); } imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, ($this->resize_width)/$ratio, $this->width, $this->height); } else { $newimg = imagecreatetruecolor(($this->resize_height)*$ratio,$this->resize_height); if($this->type=="png") { imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127)); } imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, ($this->resize_height)*$ratio, $this->resize_height, $this->width, $this->height); } } if($this->type=="png") { imagesavealpha($newimg, true); imagepng ($newimg,$this->dstimg); } else { imagejpeg ($newimg,$this->dstimg); } } //初始化图象 private function initi_img() { if($this->type=="jpg") { $this->im = imagecreatefromjpeg($this->srcimg); } if($this->type=="gif") { $this->im = imagecreatefromgif($this->srcimg); } if($this->type=="png") { $this->im = imagecreatefrompng($this->srcimg); } } //图象目标地址 private function dst_img($dstpath) { $full_length = strlen($this->srcimg); $type_length = strlen($this->type); $name_length = $full_length-$type_length; $name = substr($this->srcimg,0,$name_length-1); $this->dstimg = $dstpath; } } ?>
使用
使用时，直接调用类的构造函数即可，构造函数如下：
$resizeimage = new resizeimage($imgPath, $width, $height, $isCut, $savePath);
参数
$imgPath：原图片地址
$width：缩略图宽
$height：缩略图高
$isCut：是否裁剪，bool值
$savePath：缩略图地址（可以跟原图片地址相同）
示例
<"ResizeImage.php"; //jpg $jpgResize = new ResizeImage("img/test_1920_1200.jpg", 320, 240, false, "img/test_320_240.jpg"); //png $pngResize = new ResizeImage("img/test_1024_746.png", 320, 240, false, "img/test_320_240.png"); ?>
效果
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